During the processing of a substrate in the plasma processing chamber, satisfactory results often require tight control of the process parameters. This is particularly true for processes such as deposition, etching, cleaning, etc., that are employed to manufacture modern high density integrated circuits. When the processing parameters (such as bias voltage, RF power, ion flux, plasma density, pressure, etc.) exceed a narrow, pre-defined window, a process excursion is said to have occurred. These process excursions represent undesirable events that often lead to undesirable processing results (e.g., poor etch profile, low selectivity, etc.). Accordingly, the detection, characterization, and avoidance of process excursions are important tasks for process engineers in the manufacture of integrated circuits.
Detecting process excursions is often performed via monitoring of various process parameters. Some process parameters (such as bias voltage, reflected power, etc.) may be measured directly while others may be inferred from measured parameters.
Plasma instability faults often caused by, for example, transitions and ground delivery faults, represent a type of process excursion that has the potential to decrease yield, damage the substrate and/or damage the chamber components. Furthermore, unconfined plasma occurrences, which tend to negatively impact yield and tend to shorten the expected lifetime of chamber components, are often preceded by plasma instabilities.
Accordingly, the detection of plasma instabilities is important for the purpose of diagnostic and recipe adjustment in order to improve process results and process yield, as well as to avoid damage to the substrate and/or the chamber components.